In vivo effects of prostaglandin E2 and arachidonic acid on phagocytosis of fluorescent methacrylate microbeads by rat peritoneal macrophages

Several studies have suggested that prostaglandin E2 (PGE2) might influence the phagocytic activity of macrophage cells. The present study was designed to examine the in vivo effects of PGE2, the prostaglandin synthesis inhibitor meclofenamate, the prostaglandin precursor arachidonic acid, and the biologically inactive fatty acid 11,14,17-eicosatrienoic acid on phagocytosis by peritoneal macrophage cells in the rat. Following 3 days of treatment with either agent, fluorescent methacrylate microbeads were injected intraperitoneally into all rats. Peritoneal exudates were harvested after administration of the microbeads and the percent phagocytosis determined in macrophage cells using a fluorescence-activated cell sorter (FACS II). The administration of PGE2 was associated with a significant decrease in the percentage of peritoneal macrophages ingesting the fluorescent methacrylate microbeads. In contrast, treatment with arachidonic acid or 11,14,17-eicosatrienoic acid significantly enhanced the percentage of phagocytic macrophage cells. A significant increase in the number of macrophages undergoing phagocytosis of the methacrylate microbeads was also observed in rats treated with meclofenamate. This later observation, taken together with the inhibitory effect induced by PGE2 on macrophage phagocytosis, points to a potential modulator role of PGE2 on the phagocytic activity of macrophages. These data also suggest that arachidonic acid might influence macrophage phagocytosis by a mechanism independent of PGE2.